Preparation of mono-ethers of



Patented Oct. 23, 1951 PREPARATION OF MONO-ETHERS F 1-4-DIHYDROXYNAPHTHALENE Carl Mayn Smith, E'aston, Pa., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application December 1, 1948, Serial No. 62,973

7 Claims. 1

This invention relates to a process for preparing mono-ethers of 1,4-dihydroxynaphthalene.

The mono-ethers of 1,4-dihydroxynaphthalene, particularly the lower alkyl mono-ethers thereof, are valuable intermediates in the synthesis of certain vat and azo dyestuffs. However, no satisfactory method for their preparation has heretofore been available, and accordingly, the use of compounds of this type has heretofore been quite restricted.

Since the mono-methyl ethers of 1,4-dihydroxynaphthalene have generally been used, the present invention will be described with particular reference to their preparation. However, as

pointed out in greater detail below, my process is applicable to the preparation of mono-ethers of 1,4-dihydroxynaphthalene and aliphatic, alicyclic, aromatic and heterocyclic alcohols.

One of the methods that has heretofore been suggested for the mono-methylation of 1,4-dihydroxynaphthalene involves allowing a mixture of this substance and methyl alcohol containing hydrogen chloride to stand at room temperatures (German Patent 173,700). This reaction proceeds very smoothly but gives a yield of approximately 60% of theory. The 1,4-dihydroxynaphthalene used in the foregoing mono-esterification reaction could be prepared by reduction of 1,4-naphthoquinone for instance by treatment of 1,4- naphthoquinone with aqueous stannous chloride and HCl (Russig, J. pr. Chem., vol. 62, page 33). This reaction proceeds very smoothly if the naphthoquinone is very finely dispersed for instance by ball milling with a suitable dispersing agent, or if aqueous methanol is used to obviate the necessity of dispersing the naphthoquinone, and results in the direct isolation of yields of 80 to 85% which can be increased to 90 to 95% by treatment of the mother liquor.

The fact that naphthoquinone can be reduced in the presence of methanol suggested to me that both the reduction and mono-methylation reactions might be carried out in a single step by using a mixture of methanol with stannous chloride and hydrogen chloride. I discovered that this combined reduction and methylation reaction takes place very smoothly, giving approximately 60% yields of 4-methoxy-1-naphthol provided dry methanol, dry stannous chloride and dry HCl are used. The reaction proceeds either at room temperature or can be run in a much shorter time at reflux temperature. However, it appears that 60 to 65% is the maximum yield which can be obtained by this procedure. If milder conditions or shorter reaction times are used, the crude product contains increasing amounts of unmethylated naphthalene diol, while if the concentration of hydrochloric acid be increased or the reaction time extended, almost quantitative yields of the dimethyl ether can be obtained.

I have now discovered that if instead of using gaseous HCl as such in the above reaction I employ phosphorus oxychloride as the source of HCl, I am able to obtain in one step a yield of over 90% of theoretical of the mono-ether of 1,4- dihydroxynaphthalene of good quality. Briefly stated therefore, my process involves heating a mixture of an alcohol, phosphorus oxychloride, stannous chloride and 1,4-naphthoquinone. The lA-naphthoquinone is reduced to 1,4-dihydroxynaphthalene and mono-etherified to the corresponding mono-ether of 1,4-dihydroxynaphthalene in one step, with a yield of 90% or higher of the desired mono-ether. It was found that in carrying out the reaction in this manner it was unnecessary to employ either anhydrous stannous chloride or dry methanol and, in' addition, that the methylation stopped at the mono stage so that there was obtained in one step a 90% yield of material suitable for use, compared with an overall yield of about 50% for two steps of known process.

Phosphorus oxychloride appears to be unique in its action in this reaction since such substances as phosphorus trichloride and pentachloride, sulfuryl chloride, thionyl chloride and chlorosulfonic acid have also been tested but were found to be inferior to, or no better than dry compressed I-lCl. The reason for the unique action of phosphorus oxychloride in this reaction is not fully understood. Undoubtedly, the mixing of methanol and phosphorus cxychloride in the reaction mixture leads to the formation, to some extent, of the methyl esters of phosphoric acid and chlorphosphoric acid as Well as hydrogen chloride (gas), and it may be that a by-product of this type catalyzes the reaction or is the active reactant. However, I do not wish tobe held to any theory of operation.

As previously indicated, the reaction need not be carried out under completely anhydrous conditions since some moisture can be tolerated. Thus, in practicing the present invention ordinary (wet) methanol and hydrated stannous chloride can be used to good advantage. It will be apparent that moisture which may be present would be removed by reaction with phosphorus oxychloride. However, while extreme precautions the need not be taken to keep the reaction mixture the product.

anhydrous, it is preferable to carry out the reaction under substantially anhydrous conditions,

except for such moisture as may be introduced It has been found that the ratio .of :reactants employed in the process of this in-ven'tion can be varied widely. However, in order to obtain maximum yields of product, thenaphthoquinone, stannous chloride dihydrate and phosphoruspxychloride are employed in amounts corresponding at least to the theoretical. If desired, somewhat larger amounts of stannous chloride dihydrate and ;the phosphorus oxychloride :can be :used, but

iarenot necessary. In generaLitzis preferable :to employ an amount .of alcohol in .excess .of that theoretically required, and it has-been *found deisirable to use a ratio of alcohol tonaphthoquinone ranging from about :1 to as high as :;l, the .alcohol thus. serving the .dualfunction. as a .dilu- Lent as well as-:a.reactant.

The details of the present invention will ;be apparent. from the consideration of thefollowing specific example in which the parts-.are byfiweight.

Example A reactor fitted with a .stirrer, thermometer, dropping funnel and reflux condenser was charged with 275 parts of. methanohand ,there was then .addedslowly, with stirring, .64 partsof phosphorus oxychloride. When the, additionwas complete, the mixture was cooled .toroom .tem- .perature .and 517.5 parts .of .stannous .chloridedihydrate was added,.followed by ..30,parts..of.l ,4- naphthoquinone. The reaction mixture wasthen heated to reflux temperature, .30 to. 35.C.,.for .65 minutes, during which time the temperaturerose rapidly to a final temperature of 68 .to 3 .C. as the volatile methyl chloride Wasdistilled off through the top of the reflux condenser. The reaction mixture was then drowned, Withstirring, 'in.6000 parts of water containing .390 parts of concentrated hydrochloric acid tonprec'ipitate After filtration and drying, .there was obtained30.3 parts of l-methoxy l hydroxynaphthalene which corresponds 1103.92 92; of'the theoretical. The thus obtained .productwas of satisfactory purity for use as an intermediate in the synthesis of dyestufis.

If desired, the product may be 'furtherpurified by dissolving it in sufficient benzeneso .thatthe solution will not crystallize on the ,filter. ".The solution may then be heated with .a small amount of activated decolorizing carbon .(Nucharliiltereii and the major portion of thebenzene removed by boiling. The residual concentrate of liquor may then be diluted with 4 to 5 times its volume of hot boiling petroleum ether cooled and filtered. Recovery of the product, which consists of almost white needles, is about to The resulting product has a melting point of 128 :It will be apparent that by selection of the particular alcohol which is employed in the process, a wide variety of mono-ethers of 1,4-dihydroxynaphthalene may readily be obtained. It

jhasjbeen found that the process is operable when employing aliphatic, alicyclic, aromatic and heterocyclic alcohols. As examples of alcohols which .may:be:employed in place of the methanol specified'in the foregoing example, in order to produce correspondi g mono-ethers, may be mentioned ethanol,- Z-propanol, l-propanol, allyl alcohol, l-butanol, 3-butinol-l, Z-butanol, Z-pentanol, cyclohexanol, benzyl alcohol, phenyl ethyl alcohol and tetrahydrofurfuryl alcohol. The reaction products which can be :preparedby my process by selectionof the alcohol thus include 11-ethoxy-4- naphthol, -cyclohexyloxy-l-naphthol, .4-.benz yloxy-l-naphthol and 4-tetrahydrofurfuryloxylenaphthol, etc.

I-claim:

1. The process of producing mono-ethers -:of 1,4-dihydroxynaphthalene which comprises heat- ,ing a mixture of a monohydroxy alkane, phosphorus oxychloride, stannous chloride and 1,4- naphthoquinone.

.2. The process as defined in claim 1,-wherein the monohydrox-y alkane is employed insubstantial excess.

3. The process of producin loweralkyl ,mono- 'ethers of 1,-dihydroxynaphthalene, whichcomprises heating a mixture of a monohydroxy l wer alkane, phosphorus oxychloride, stannouschlo- :ride and lA-naphthoquinone.

A. The process as .definedin claim 3, wherein ;a substantial excess of the --;monohydroxy ilower alkane specified is employed.

v5. The process of producing -4-metho-xy-1- naphthol, which comprises hea-ting amixtuigepf methanol, phosphorus .oxychloride, stannous .chloride dihydra-te and ,lA-naphthoquinone.

.6. Theprocess as defined in claim 5, wherein ;a substantial excess of' methanol is -emplQ-y6d.

7. The process as defined claim l, wherein thereaction is carried outunder-substantially anhydrous-conditions.

:QARL -MAYN SMITH.

REFERENCES CITED The. following references are of record ,inethe 151.8 of this patent:

'Rus sig: -Jour. Prak. Chem.; .vol. 162, 1900, Pa es 32 33.

Number 

1. THE PROCESS OF PRODUCING MONO-ETHERS OF 1,4-DIHYDROXYNAPTHALENE WHICH COMPRISES HEATING A MIXTURE OF A MONOHYDROXY ALKANE, PHOSPHORUS OXYCHLORIDE, STANNOUS CHLORIDE AND 1,4NAPTHTHOQUINONE. 